The present invention relates to a motor core formed by a plurality of split core pieces arranged in an annular shape, a stator having the motor core, and a method for manufacturing the stator.
Conventionally, a stator mounted in a brushless motor or the like includes an annular motor core, which has a plurality of radial teeth. A coil is wound around each of the teeth. The ends of each corresponding pair of the coils are electrically connected to each other through a bus bar, which is mounted in the stator.
As described in Japanese Patent No. 4444639, an annular motor core for a stator is configured by a plurality of split core pieces, each of which includes a yoke portion extending in a circumferential direction of the motor core and a tooth extending substantially perpendicular to the yoke portion. The split core pieces are circumferentially located and arranged in an annular shape. Each of the split core pieces is formed by stacking two types of core sheets alternately in the axial direction. Each of the core sheets includes a yoke forming portion, which is laminated with another yoke forming portion to form the yoke portion, which extends in the circumferential direction of the motor core. Each of the yoke forming portions has opposite circumferential ends, one of which is referred to as a first end located at a first circumferential side, with the other referred to as a second end located at a second circumferential side. The two types of core sheets include a first type of core sheets and a second type of core sheets. Specifically, each of the first type of core sheets includes an arcuate projection, which projects from the first end and has an arcuate shape as viewed in the axial direction, and an arcuate recess, which is formed in the second end and also has an arcuate shape as viewed in the axial direction. Each of the second type of core sheets has an arcuate recess, which is formed in the first end and is shaped arcuate as viewed in the axial direction, and an arcuate projection, which projects from the second end and has an arcuate shape as viewed in the axial direction. Each split core piece is formed by laminating the two types of core sheets alternately in the axial direction. The corresponding circumferential ends of the yoke portions of each adjacent pair of the split core pieces are pivotably engaged with each other such that the arcuate projections of the split core pieces are overlapped alternately as viewed in the axial direction. An insulator is attached to each split core piece to ensure insulation between a coil wound around the tooth and the split core piece. Each adjacent pair of the split core pieces are pivotably joined together through the insulators. The split core pieces, which are joined together through the associated insulators, are arranged such that the interval between the distal ends of each adjacent pair of the teeth increases. In this state, a coil is wound around each of the teeth over the corresponding one of the insulators. Then, by pivoting each adjacent pair of the split core pieces, the split core pieces are arranged in an annular shape such that the yoke portions form an annular shape as a whole and that the distal ends of the teeth all face radially inward with respect to the annular shape. When the split core pieces are arranged in the annular shape, the coils are arranged in a circumferential direction.
As described in Japanese Patent No. 3430839, corresponding ends of multiple coils of a stator are electrically connected together through a plurality of bus bars. Each of the bus bars is formed by a linear coated conductive wire, the outer periphery of which is coated by an insulating membrane, and has an arcuate shape. Each bus bar is held by a circular holder. A connection wire, which extends radially to project radially outward from the holder, is formed at each of the opposite ends of each bus bar. The holder is arranged at the side corresponding to an axial end of a motor core, in which the coils are mounted, thus arranging the bus bars at the side corresponding to the corresponding axial ends of the coils. Each of the connection wires and the end of the associated one of the coils are arranged parallel to each other at a position radially outward relative to the holder. In this state, a connection terminal is mounted on the connection wire and the end of the coil, which are parallel to each other, to cover the outer periphery of the connection wire and the outer periphery of the end of the coil. The connection terminal, the connection wire, and the end of the coil are swaged to electrically connect the connection wire to the end of the coil. As has been described, the bus bars described in Japanese Patent No. 3430839 are formed by the linear coated conductive wires. This reduces waste of the material and increases the yield.
However, in the motor core described in Japanese Patent No. 4444639, the corresponding circumferential ends of the yoke portions of each adjacent pair of the split core pieces are engaged with each other such that the arcuate projections of the split core pieces are alternately overlapped as viewed in the axial direction. As a result, when the adjacent split core pieces are pivoted relative to each other, the arcuate projections of the split core pieces slide over each other. This causes the mutually engaged yoke portions to slide on each other, thus producing friction, which hampers pivot of the split core pieces. The split core pieces are arranged in an annular shape, or, in other words, subjected to annular arrangement, in the state in which the interval between the distal ends of each adjacent pair of the teeth is increased (for example, the state in which the split core pieces are aligned linearly such that the teeth extend parallel to one another). In other words, the annular arrangement of the split core pieces is performed in a state greatly different from the state in which the split core pieces are circumferentially arranged to form an annular motor core. This complicates the annular arrangement of the split core pieces, thus making it difficult to carry out a step for arranging the split core pieces in an annular shape.